An organic light-emitting diode (“OLED” for short) display has advantages of active light emission, good temperature characteristics, low power consumption, fast response, bendability, ultralight weight, ultrasmall thickness and low cost, etc., and has been widely used in display devices.
OLED displays can be divided into three types depending on the light-emitting direction: bottom emitting OLEDs in which light is emitted in a direction from a backplate, top emitting OLEDs in which light is emitted in a direction from the top of the device, and double-sided emitting OLEDs in which light is emitted in a direction simultaneously from both the substrate and the top of the device. The top emitting OLED is independent of whether the substrate can transmit light or not, and can effectively improve the aperture ratio of the display panel, facilitates the integration with a transistor backplate, and can also narrow the spectrum and improve color purity. Therefore, the top emitting OLED is widely applied to flat panel displays.
However, many studies have shown that output efficiency of light of the top emitting OLED is low, i.e., external quantum efficiency is low, and usually only 20% at the highest level. Factors that affect the output of light may be roughly divided into four types: waveguide effect, substrate effect, surface plasma effect and absorption effect.